Stone to Bowl. Copper smelting

Finally I am three weeks into my Stone to Bowl residency and I feel that I should share progress.

One element of Stone to Bowl is to develop a replicable way of smelting copper from malachite/copper ore in a traditional way that means that I can work in the landscape anywhere.

First task was to source some Scottish copper ore. The mine in Bridge of Allan is long closed, but I found some copper traces on the waste heap. These photos show the mine entrance and the pieces that I collected.

After initial smelting experiments I have been putting the ore in closed ceramic  balls with added charcoal to give a reducing atmosphere for the smelt. (While I was on my residency another artist was successfully smelting malachite using oxy-acetylene.)

The furnace is charcoal burning; and for these experiments I was using an electric air blower, although I will use bellows when I understand the process more. The dry ceramic balls are made of a local refractory clay mixed with fibre -horse dung, and sand. Inside is copper ore in pea size chunks  with 25% charcoal. The balls are placed on the furnace charcoal once it is burning well and the furnace is run until the ore is to a high enough temperature to smelt, hopefully. The balls are then plunged into water and broken open.

The first smelt was not a complete success. Some copper was formed, but a lot of this was pelletised rather than consolidated and some had to be panned from the ashes of the furnace.

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However I reheated this copper to consolidate it and a reasonable amount of copper was retrieved. Again I used an electric furnace for this process while I am experimenting.

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I am not sure that a chimney furnace is needed, a horseshoe hearth might be as successful as one can see what is going on. The chimney furnace is made of a refractory clay mix similar to that used for the balls.

I tried another smelt later in the residency of which more anon.

Stone to Bowl

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Following further research I have made up some clay balls with a mixture of malachite and charcoal inside to smelt. Copper results from removing oxygen from the copper ore, so the sealed clay balls should be more successful that the pit smelt that I did at the Sculpture Workshop.

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I like the way the clay balls look a bit like poppy seed heads.

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I’ll let them dry out a bit before I try and get them to smelting temperature in a charcoal furnace.

VACMA support acknowledgement-text + logost

 

Stone to Bowl

VACMA support acknowledgement-text + logost

I have been awarded funding for my Stone to Bowl project. It will pay for several weeks at the Scottish Sculpture Workshop in 2018 to complete the project which will take copper ore through to cast pieces, using traditional and fully sustainable methods.

I’ve been doing some preparatory work:-

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I experimented with melting the copper that I pit-smelted this year at the Sculpture Workshop, adding in some silver to lower the melting temperature. I melted 115gm and got 74gm of copper and some residual oxides which didn’t melt. The left hand metal is copper, the right is the original smelt material which is less pure. Next trial will be to sand cast with the copper/silver alloy.